1. Field of the Invention
The present invention relates generally to linearization of voltage controller oscillators (VCOs).
2. Background Art
Conventionally, VCOs use MOSFET variable capacitors (varactors) and thus are inherently non-linear.
Various calibration methods exist for linearizing VCOs. For example, one technique attempts to operate the VCO in a linear region of its gain response function. However, this technique only works for small signal modulation and does not work when modulating wide bandwidth signals, such as WCDMA and EDGE signals, for example. Another technique uses a set of varactors biased in a staggered fashion so as to generate in the aggregate a linear transient response of the VCO. However, this technique does not address VCO gain variations due to process, voltage, and temperature (PVT) variations. In addition, because each varactor requires a clean reference voltage for operation, implementation of this technique is both difficult and expensive.
Thus, conventional VCO gain linearization techniques are not suitable for generating complex wide bandwidth waveforms, cannot handle PVT variations, and are relatively difficult and expensive to implement.
Accordingly, there is a need for improved methods and systems for linearizing the gain of a VCO.